The present invention relates generally to spinal fixation devices for the internal fixation of the spine particularly within the fields of orthopedics and/or neurosurgery such as spinal implants and rods for holding vertebral bones fixed relative to one another and, more particularly, to a polyaxial pedicle screw and/or coupling apparatus for use in spinal surgical procedures for receiving a rod for stabilizing the relative motion of vertebrae.
The spinal column of bones is a highly complex structure that not only allows a high degree of flexible movement in various directions, but also envelopes and protects numerous veins, arteries and nerves of the body. The adult human spine consists of over twenty discrete bones that are coupled sequentially to one another through posterior facet joints and discs of cartilage (known as intervertebral discs or simply, discs) positioned between adjacent vertebrae. The facet joints and discs allow the spine to bend and twist. Different muscles coordinate movement in many directions.
Areas of the spine have been anatomically categorized. Thus, bones of the spine are anatomically classified as being from one of four areas or classifications, namely, the cervical, thoracic, lumbar, or sacral areas. The various areas of the spine also have a natural or characteristic curvature or curve. The four curves of the spine are known as the cervical lordosis, the thoracic kyphosis, the lumber lordosis and the sacral kyphosis.
Genetic or irregularities such as developmental irregularities, trauma, tumors, disease and the like, however, can result in spinal pathologies that either limit the range of normal spinal motion or that threatens the integrity of elements of the nervous, circulatory and/or other systems of the spine. In these cases and others such as spinal curvature problems, a spinal fixation system may be used in order to immobilize various vertebrae. Various systems have been devised to provide the necessary vertebrae immobilization. These spinal fixation systems are implanted on or in the spine (spinal column). Such spinal fixation systems or assemblies may be classified as anterior, posterior or lateral implants. Lateral and anterior fixation assemblies are attached to the lateral and anterior portions of the spine. Posterior implants generally include a pair of rods that are along the axis to which the vertebrae are to be disposed and then attached to the vertebrae by either hooks that couple to the lamina or transverse process of the vertebrae, or by screws that are inserted into the pedicles thereof.
Rod assemblies as spinal fixation systems generally comprise a plurality of bone or pedicle screws that are implanted into the posterior lateral surfaces of the laminae, through the pedicles and into their respective vertebral bodies. Each screw includes a coupling device for receiving and retaining a section of a spinal rod. The rod extends along the axis of the spine being attached to the plurality of pedicle screws through their respective coupling device. The rigidity of the spinal rod may be utilized to align the spine in conformance with a desired shape.
Considerable difficulty, however, was encountered with inserting fixed screws along a misaligned curvature and then simultaneously exactly positioning the coupling devices such that the spinal rod receiving portions of the coupling devices were aligned such that the spinal rod could be passed therethrough without distorting the screws. Because of such difficulty, polyaxial screw and coupling devices have been developed that allow limited movement of the coupling device relative to the implanted screw. Once a desired position is achieved, the coupling device is fixed relative to the screw.
However, while the prior art is replete with polyaxial screw and coupling devices for spine fixation systems, they only permit a limited freedom of movement with respect to angulation of the screw and the coupling device. Moreover, these prior art polyaxial screw and coupling devices are generally complex, inadequately reliable, and lack long-term durability. Furthermore, these prior art polyaxial screw and coupling devices do not allow the independent fixation of screw to coupling device angulation and rod fixation. These considerable drawbacks associated with prior art systems also include difficulty properly positioning the rod and coupling devices, and the tedious manipulation of the many small parts in the operation environment.
In view of the above, it is therefore an object of the present invention to provide a pedicle screw and rod coupling device assembly that provides polyaxial freedom of screw implantation angulation with respect to rod reception.
It is also an object of the present invention to provide a pedicle screw construct that provides independent fixation of angulation of the rod coupling device relative to the pedicle screw and of the spinal rod to the rod coupling device.
It is further an object of the present invention to provide a pedicle screw construct that provides angular reception of the spinal rod by the rod coupling device.
Accordingly, it is also an object of the present invention to provide a pedicle screw construct and/or spinal rod fixation assembly that is reliable, durable and which gives long term spinal fixation support.
These needs and/or objects, and others are accomplished through application of the principles of the subject invention and/or as embodied in one or more various forms and/or structures such as are shown and/or described herein.